1. Field of the Invention
The present invention relates to a surface treating method and a device thereof for generating air bubbles due to cavitation (hereinafter, referred to as “cavitation bubbles”), by sucking in or suck in and spraying fluid via a narrowed portion provided at midstream of a flow passage, and for acting an impact force caused by crushing the cavitation bubbles (hereinafter, referred to as “a crushing impact force”) on a treated surface in the vicinity of the narrowed portion.
2. Background Art
Conventionally, there is well known a technology for performing a surface modification which improves material property such as fatigue strength, by processing a surface of a nonmetallic material such as a metal material, a plastic, a glass or a semiconductor due to local material removal such as grind, or by pressing the surface thereof so as to add compressive stress to it, or alternatively, for performing various treatments such as the processing, the surface modification, the washing (hereinafter, referred to as “a surface treating”), by vigorously spraying a jet flow of high pressure fluid containing the cavitation bubbles (hereinafter, referred to as “a spraying cavitation flow”) onto the surface of the treated material (hereinafter, referred to as “a treated surface”) and by acting the treated surface on the crushing impact force of the cavitation bubbles, for the purpose of removing and washing attached impurities. The surface treating technology can deal with previous problems, such as the problem of environmental pollution, device corrosion due to wet etching which uses etching fluid having high oxidation nature, the problem of difficulty in applying to the severe working environment, the surface roughening of a low intensity member due to a blast process for intensively blasting fine abrading agent or the like together with high-pressure air, the problem of increasing size of a pump or the like, increasing cost of devices due to a water-jet machining for performing a cutting by using a jet flow of high-pressure water through small holes or the like, and the problem of difficulty in applying to complicated shapes due to machining process such as cutting, grinding, polishing.
As a result of keen examinations, the inventers or the like disclose the surface treating technology, which generates a flow with the cavitation bubbles, by sucking in processing fluid with a pump and by locally limiting a flow of the processing fluid while sucking in by a narrowed portion provided on the processed surface, so as to cause the cavitation at the downstream side of the narrowed portion, and which applies a flow of the processing fluid containing the cavitation bubbles generated at this time (hereinafter, referred to as “a sucking cavitation flow”) to the processed surface (for example, see nonpatent literature 1). According to the surface treating technology, an influence of excess localized pressure due to the jet flow of the processing fluid can be minimized, and a surface roughening of the processed surface remains small, so as to perform the high-precision processing, unlike in the previous case of locally, vigorously spraying the spraying cavitation flow onto the processed surface. Further, colliding force when particulates on which the crushing impact force acted clashes with the processed surface is added, except for the crushing impact force of the cavitation bubbles, by distributing and mixing the particulates to the processing fluid, so that a processing efficiency of the processed surface can be significantly improved.
Nonpatent literature 1: Kazuhito OHASHI, et al., “A microfabrication method using a sucking cavitation flow”, Japan Society for Precision Engineering, spring convention, academic lecture meeting, collection of papers, 2005 Mar. 1, Hei 17, pp 1307 to 1308.